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Flashcards in Biochem Week 8 Deck (30)
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1
Q

What is fermentation to a biochemist?

A

Anaerobic process that generates energy by the breakdown of organic compounds.

2
Q

What is fermentation in industry?

A

Any aerobic process that produces microorganisms (biomass) as the end product.

Transformation of a compound by microbial cells.

3
Q

What are biochemical engineers responsible for in fermentation?

A

To ensure that microorganisms can be grown in large quantities under the conditions that give optimal product yield.

4
Q

Definition of a bioreactor

A

Aerobic and anaerobic microorganisms are cultured under controlled conditions in a large chamber. This is a bioreactor or fermenter.

5
Q

Processes of fermentation.

A
  1. Batch Fermentation
  2. Fed-Batch Fermentation
  3. Continuous Fermentation
6
Q

The mechanism of batch fermentation

A

The sterile growth medium is inoculated with the appropriate microorganisms and the fermentation proceeds without the addition of fresh growth medium

7
Q

The properties within batch fermentation

A

The composition of culture medium, concentration of microorganisms, the internal chemical composition of microorganisms and amount of metabolite all change during fermentation

All phases of bacterial growth cycle are observed.

8
Q

The mechanism of fed-batch fermentation

A

Fresh growth medium is added continuously during fermentation and no growth medium is removed until the end of the process.

9
Q

Which phases does the continuous addition of medium affect?

A

It prolongs the stationary and log phases, thereby increasing the biomass and the amount of metabolites.

10
Q

How does fed-batch compare to batch fermentation?

A

A fed-batch fermentation strategy can increase the yield from 25% to more than 1000%.

11
Q

How to control the addition of feed in fed-batch fermentation?

A

Fed-batch fermentation is a system in which nutrient is added when the concentration falls below some set point. The best way to control the addition is to monitor the concentration of the nutrient itself in the fermenter or reactor vessel so know exactly how much needs to be added.

12
Q

When is the fed-batch strategy used?

A

It is used in bio-industrial processes to reach a high cell density in the bioreactor.

13
Q

Is the feed solution concentrated or dilute?

A

Mostly the feed solution is highly concentrated to avoid dilution of bioreactor.

14
Q

The primary benefit of the controlled addition of a nutrient

A

It directly affects the growth rate of the culture and helps to avoid the overflow metabolism.

15
Q

Why is the nutrient is added in several doses?

A

To ensure that there is not too much nutrient present in the fermenter at any time. If too much of a nutrient is present, it may inhibit cell growth. By adding a little at a time, the reaction can proceed at a high rate of production without getting overloaded.

16
Q

Examples of fed-batch in industry

A
  • Saccharomyces cerevisiae - maintains glucose at very low concentration, maximises biomass yield, minimises ethanol production.
  • Penicillin production.
  • Hepatitis B surface antigen which is used as a vaccine. Purified from human plasma and expressed in recombinant yeast.
17
Q

How does fed-batch compare to batch and continuous fermentation?

A

It is in between batch and continuous fermentation

18
Q

Advantage of fed-batch

A
  • Production of high cell densities due to extension in working time.
  • Controlled conditions in provision of substrates
  • control over production of by-products due to limited provision of substrates solely required for product formation
  • allows replacement of water loss by evaporation
  • alternative mode of operation for fermentations leading with toxic substrates
  • no additional special piece of equipment is required compared with batch fermentation
19
Q

Disadvantage of fed-batch

A
  • It requires previous analysis of microorganisms, its requirement and understanding of physiology with productivity.
  • substantial amount of operator skill in set-up, definition and development of process.
  • cyclic fed-batch culture, care should be taken to design a process to ensure that toxins do not accumulate to inhibitory levels.
20
Q

What is the optimal strategy of fed-batch fermentation?

A

Feed the growth-limiting substrate at the same rate that the organism utilises the substrate.

21
Q

How to balance substrate feed and demand?

A
  1. open loop control schemes in which feed is added according to historical data
  2. indirect control of substrate feed based on non-feed source parameters such as pH, offgas analysis etc
  3. indirect control schemes based on mass balance equations
  4. direct control schemes based on direct, on-line measurement substrates.
22
Q

How is more flexible control obtained?

A

When there is direct measurement of a substrate or excreted metabolite In the medium. This is used to influence feeding rates of fermentation. This can be done off-line or semi on-line

23
Q

Why are on-line measurements more useful?

A
  • shorter analysis required
  • lower personnel requirement
  • reduced chance of fermenter contamination
24
Q

What influences the control and optimization of bioreactors?

A

It is strongly influenced by quality of sensors available for crucial response variables. Of primary importance is ratio of dynamic parameters of sensor to those of process. When variables cannot be measured easily or quickly enough, a mathematical model must be used in some way in place of feedback information.

25
Q

How is the feed rate calculated in a bioreactor?

A

F = (muVx)/(Y*[Gly])
F is feed rate (L hr-1)
mu is specific target growth rate (hr-1)
V is fermenter volume (L)
x is cell biomass (grams of dry cell weight L-1)
Y is yield of cell mass per unit carbon source of glycerol.
[Gly] is concentration of glycerol feed solution (g L-1)

26
Q

How to measure the optical density?

A

A spectrophotometer is used to measure how much light is blocked out by bacteria in suspension

27
Q

What units are used?

A

OD units (absorbance) rather than Klett Units

28
Q

The correlation between the optical density (OD) and the cell number?

A

Due to size and shape the amount of light blocked out is unique to each species.
We must develop a correlation between the absorbance and colony forming unit (number of cells) per ml

29
Q

What is the respiratory quotient?

A

QR = moles of CO2 product/ moles of O2 reactant

30
Q

When is fed-batch used?

A

To avoid repressive effects of high substrate concentration.

To control the organism’s growth rate and consequently controlling oxygen demand of fermentation.